The Center for Clinical Epidemiology and Biostatistics (CCEB) of the University of Pennsylvania (Penn) School of Medicine submits this renewal application to continue and expand an innovative and successful post- doctoral training program in clinical pharmacoepidemiology (i.e., the use and effects of medications in populations). Penn promotes an academic environment in which basic and clinical research are encouraged and viewed as attractive career paths for trainees. This training program attracts clinical pharmacoepidemiology trainees from other institutions nationwide. It is anticipated that many graduates of this training program will be placed in other institutions nationwide, resulting in a program of the highest impact. The two- to three-year training program consists of required courses in clinical epidemiology, research methodology, biostatistics, pharmacoepidemiology, pharmacokinetics; elective courses in pharmacology, pharmacy practice, or other areas relevant to the trainees' interests and experience; extensive independent readings; participation in research seminars at the CCEB; clinical experiences in clinical pharmacology; and the completion of a mentored independent research project in clinical pharmacoepidemiology. The program is designed to: 1) train clinicians to be rigorous and independent academic investigators able to use the range of approaches available in epidemiology to address research issues in clinical pharmacoepidemiology related to the etiology, prognosis, prevention and early detection, treatment, clinical economics, technology assessment, medical decision making, and quality of patient care; 2) provide an understanding of the basic principles of clinical pharmacology; 3) provide intensive, supervised research experience with mentors in clinical pharmacoepidemiology; 4) provide closely mentored research experiences with faculty preceptors in clinical pharmacoepidemiology; and 5) strengthen the links between traditional epidemiology and clinical pharmacology. With the expansion of this training program, five fellowship slots will be awarded each year. Trainees matriculate in the Master of Science in Clinical Epidemiology (MSCE) degree program. Strengths of the proposed program are: 1) the large pool of extremely strong candidates seeking training in pharmacoepidemiology; 2) the long history of successful research training programs in the CCEB, including the internationally renowned clinical pharmacoepidemiology program and overlapping training in comparative effectiveness research (a new area of interest to NIH); 3) the comprehensive course offerings and research programs available to trainees; and 4) the successful training records of the program directors and faculty. In addition, the availability of the CCEB faculty, who provide expertise in a wide range of disciplines; numerous large databases useful for research projects and training; a broad array of specialized analytic capabilities available for clinical studies (e.g., clinical trials, case-control, cohort research, etc.); and the faculties' commitment to collaborative research and training, combine to provide an ideal environment for this program.